Systems and methods for RFID-enabled pressure sensing apparatus

ABSTRACT

Methods, apparatuses and systems for radio frequency identification (RFID)-enabled information collection are disclosed, including an enclosure, a collector coupled to the enclosure, an interrogator, a processor, and one or more RFID field sensors, each having an individual identification, disposed within the enclosure. In operation, the interrogator transmits an incident signal to the collector, causing the collector to generate an electromagnetic field within the enclosure. The electromagnetic field is affected by one or more influences. RFID sensors respond to the electromagnetic field by transmitting reflected signals containing the individual identifications of the responding RFID sensors to the interrogator. The interrogator receives the reflected signals, measures one or more returned signal strength indications (“RSSI”) of the reflected signals and sends the RSSI measurements and identification of the responding RFID sensors to the processor to determine one or more facts about the influences. Other embodiments are also described.

I. ORIGIN OF THE INVENTION

The invention described herein was made by employees of the UnitedStates Government and may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

II. BACKGROUND OF THE DISCLOSURE

The embodiments described herein relate generally to the field of radiofrequency identification (“RFID”).

III. SUMMARY

The embodiments described herein relate to applications of radiofrequency identification (RFID) technology to monitor and manageinventory, including RFID-enabled dispensers, which permit tracking ofsmall items, such as pills or grains, for which attachment of individualRFID sensors is impractical. Other inventory management applicationsinclude level detectors, in which the level of material filling a volumeis sensed. Sensor applications include a distributed pressure sensor.

Methods, apparatuses and systems for RFID-enabled information collectionare disclosed, including a system comprising an enclosure, a collectorcoupled to the enclosure, an interrogator, a processor, and one or moreRFID field sensors, each having an individual identification, disposedwithin the enclosure. The interrogator is configured to transmit anincident signal to the collector, causing the collector to generate anelectromagnetic field within the enclosure. The electromagnetic field isaffected by one or more influences. One or more of the RFID sensorsrespond to the electromagnetic field by transmitting, via the collector,a reflected signal to the interrogator, the reflected signals containingthe individual identifications of the responding RFID sensors. Theinterrogator is configured to receive the reflected signals, measure oneor more returned signal strength indications (“RSSI”) of the reflectedsignals and send the RSSI measurements and the correspondingidentification of the responding RFID sensors as information to theprocessor. The processor is configured to analyze the information todetermine one or more facts about the influences.

Another embodiment disclosed is a RFID-enabled dispenser including aparallel plate waveguide comprising a plurality of conductive layers anda dispensing container placed within the waveguide. The dispensingcontainer has an opening for dispensing items and a dispensing elementfor moving the items to be dispensed through the opening. The dispensingcontainer also has a traveler for moving items within the dispensingcontainer towards the opening, the traveler moving in response to forceexerted by a forcing element. An antenna, coupled to the waveguide, isconfigured to generate an electromagnetic field within the waveguide inresponse to an incident signal sent from an interrogator, theelectromagnetic field being affected by one or more influences. One ormore RFID field sensors are placed inside the waveguide at intervalsalong the axial direction of the waveguide. Each RFID field sensor hasan identification and is capable of responding to the electromagneticfield by transmitting, via the antenna, reflected signals to theinterrogator, the reflected signals containing the identification of theresponding RFID field sensors. The interrogator is further configured toreceive the reflected signals, measure one or more returned signalstrength indications (RSSI) of the reflected signals and send the RSSImeasurements and the corresponding identification of the responding RFIDfield sensors as inputs to the processor for use by the processor inmaking at least one determination about the one or more influences.

Another embodiment disclosed is a RFID-enabled dispenser comprising aholder and a dispensing container placed within the holder. The holderhas an elongated structure with multiple antenna cells, each antennacell containing an RFID circuit having a unique identification. Eachantenna cell is of sufficient size for resonance, so that the antennacell may tune to an operating frequency of its RFID circuit. Thedispensing container has an opening for dispensing items from thedispensing container and a traveler for moving items within thedispensing container towards the opening. The traveler moves in responseto force exerted by a forcing element. The traveler includes adielectric body (which may include optional metallic or conductivecomponents), the position of the traveler and its dielectric bodyactivating a particular antenna cell in which the traveler is positionedand enabling the RFID circuit within the particular antenna cell toreceive an incident signal from an interrogator and to send a responseto the interrogator. The interrogator is configured to receive theresponse, measure one or more returned signal strength indications(“RSSI”) of the response and send the RSSI measurements and thecorresponding identification of the responding RFID field sensors asinformation to a processor. The processor is configured to use theinformation received from the interrogator to determine the position ofthe traveler. The items may comprise packages of one or more objects. Inone embodiment, for example, the items may be disk-shaped and includesegmented packaging for separating two or more of the objects.

Another embodiment described herein is an apparatus for a radiofrequency identification (RFID)-enabled pressure sensing glove,including a glove having a palm side, a back side, and at least onedigit. The glove includes a plurality of ring elements, each on a foampad, the foam pads being attached to the palm side of the glove on theat least one digit and palm, each ring element including a RFID sensorattached to a near field loop, and a microstrip patch antenna on theback side of the glove. The microstrip patch antenna is connected to oneor more microstrip lines coupling the antenna to the ring elements, themicrostrip lines each terminating in a load element near the end of eachdigit, which prevents development of a standing wave pattern. Pressureon a ring element activates its RFID sensor allowing the RFID sensor totransmit a signal to an interrogator.

Yet another embodiment described herein is an apparatus for a radiofrequency identification (RFID)-enabled pressure sensitive keypad. TheRFID-enabled keypad includes a plurality of RFID tags bonded to anoperatively insulating and compressible substrate and an operably planaropen waveguide, the waveguide being bonded on an operatively insulatingdielectric base and in communication with a collector. A load isconnected to one end of the waveguide. The substrate bearing the RFIDtags is positioned over the base and adjacent to a conductor of thewaveguide, one or more of the RFID tags being energized when operablydepressed to send signals via the collector to an interrogator, anelectromagnetic coupling being enabled between the waveguide and thedepressed RFID tag.

Another embodiment described herein is a method of determining one ormore influences on a generated electromagnetic field. The methodcomprises the step of transmitting an incident signal from aninterrogator to a collector coupled to a waveguide causing the collectorto generate the electromagnetic field along the waveguide. Theelectromagnetic field may be affected by the one or more influences. Thewaveguide contains one or more radio frequency identification (RFID)sensors, each RFID sensor having an individual assigned identification.The method further comprises the steps of transmitting a reflectedsignal from one or more of the RFID sensors via the collector to theinterrogator in response to the electromagnetic field, the reflectedsignal including the individual identification from the responding RFIDsensors, measuring one or more returned signal strength indications(“RSSI”) of the reflected signal by the interrogator, and sending theRSSI measurements and the corresponding identification of the respondingRFID field sensors from the interrogator to a processor. The methodfurther comprises the step of analyzing the RSSI measurements andidentifications by the processor to make determinations about the one ormore influences.

Another embodiment disclosed is an apparatus for use as a switch,comprising at least one RFID tag, each RFID tag comprising an antennaelement and an RFID integrated circuit, at least one source element, andat least one lever arm. Each lever arm is connected to one of the RFIDtags, and each lever arm is capable of two positions. One of thepositions places the lever arm and the RFID tag connected thereto intoalignment with the source element.

Another embodiment disclosed is a system for radio frequencyidentification (RFID)-enabled information collection comprising one ormore antenna cells comprising ring elements, each ring element includinga conductive ring connected to a RFID integrated circuit, at least onesource element, an interrogator capable of transmitting a signal to thesource element and a processor in communication with the interrogator.At least one of the conductive rings is capable of coupling to itssource element when the conductive ring is in a first position,energizing the RFID circuit associated with the conductive ring torespond to the interrogator's signal. The processor is capable ofderiving information regarding the positions and orientations of the oneor ring elements relative to the one or more sources. The source elementmay be an antenna element, or in another embodiment the source elementmay be an open waveguide, such that the ring element can couple to thewaveguide structure when it is in the proper position and/ororientation. The conductive ring and the source element may be placed ondoor components such that the conductive ring couples to the sourceelement only when the door is in a first position.

Other aspects and advantages of the embodiments described herein willbecome apparent from the following description and appended claims,taken in conjunction with the accompanying drawings, illustrating theprinciples of the embodiments by way of example only.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID-enabled enclosure in the formof a cavity comprising a container.

FIG. 2 is a schematic diagram in accordance with one or more embodimentsdescribed herein in which an RFID-enabled enclosure is in the form of acavity comprising a container and a collector comprising an antenna lidon the container.

FIG. 3 is a schematic diagram in accordance with one or more embodimentsdescribed herein of an RFID-enabled container with RFID field sensors inthe form of an array of RFID integrated circuits.

FIG. 4 depicts a schematic diagram in accordance with one or moreembodiments described herein of an RFID-enabled cavity filled with foamand bounded by a conductive fabric exterior.

FIG. 5 depicts a schematic diagram in accordance with one or moreembodiments described herein of an RFID-enabled conductive cavity inwhich a conductive, flexible diaphragm applies pressure to and reducesthe volume of the RFID-enabled conductive cavity.

FIG. 6 is a schematic diagram of an RFID-enabled item dispenser havingmultiple items in each dispensed disc, in accordance with one or moreembodiments described herein.

FIG. 7 depicts a schematic diagram in accordance with one or moreembodiments described herein of an RFID-enabled container or dispenserhaving conductive walls and a conductive center post.

FIG. 8a is an illustration of an RFID-enabled container made inaccordance with one or more embodiments described herein. FIGS. 8b-8eare illustrations depicting additional details of a capacitively-fedplanar inverted F antenna (“PIFA”), such as the one used for theRFID-enabled container of in FIG. 8 a.

FIG. 9 is a graph depicting the results of four tests performed usingthe embodiment of FIG. 8 a.

FIG. 10 is a schematic diagram of a spring-operated item dispenser.

FIG. 11 is a schematic diagram of the item dispenser of FIG. 10,modified to be an RFID-enabled item dispenser having an enclosure in theform of a parallel plate waveguide, in accordance with one or moreembodiments described herein.

FIG. 12 is a schematic diagram of an RFID-enabled item dispenser havingan enclosure in the form of a coaxial waveguide, in accordance with oneor more embodiments described herein.

FIG. 13 is a schematic diagram of an RFID-enabled item dispenser inaccordance with one or more embodiments described herein, wherein atraveler contains a dielectric body within.

FIG. 14 is a schematic diagram of an embodiment of the holder cells ofFIG. 13.

FIG. 15 is a schematic diagram of another embodiment of the holder cellsof FIG. 13, illustrated with a traveler, having a conductive pattern,within the holder cell.

FIG. 16 is a schematic diagram of an RFID-enabled item dispenser inaccordance with one or more embodiments described herein, having holdercells on two sides of the dispenser, with an electromagnetic short onone side of the holder cells.

FIG. 17 is a schematic diagram of an RFID-enabled item dispenser withthe dispensing component outside of the holder in accordance with one ormore embodiments herein.

FIG. 18 is a schematic diagram of an interrogation of an RFID-enableditem dispenser in accordance with one or more embodiments describedherein.

FIG. 19a is a schematic diagram of an RFID-enabled item dispenser,depicting an end view cross section of a dispenser unit, in accordancewith one or more embodiments described herein.

FIG. 19b is a schematic diagram of an RFID-enabled item dispenser inwhich a top conductive layer comprises a top circuit having one or morering microstrip antenna cells, in accordance with one or moreembodiments described herein.

FIG. 19c is a schematic diagram of an RFID-enabled item dispenser havinga traveler conductive layer beneath a traveler dielectric layer, inaccordance with one or more embodiments described herein.

FIG. 19d is a schematic diagram of an RFID-enabled item dispenser inaccordance with one or more embodiments described herein, in which atraveler conductive surface provides a folded ground plane with a short.

FIG. 19e is a schematic diagram of an RFID-enabled item dispenser havinga circular cross section and ring microstrip antennas, in accordancewith one or more embodiments described herein.

FIG. 19f is a schematic diagram of an RFID-enabled item dispenser havinga top conductive layer of one or more microstrip antennas wrapped arounda cylinder with a circular cross-section, in accordance with one or moreembodiments described herein.

FIG. 20 is a schematic diagram of the palm side of an RFID-enabledpressure sensor glove in accordance with one or more embodimentsdescribed herein.

FIG. 21 is a schematic diagram of the back (top) side of an RFID-enabledpressure sensor glove in accordance with one or more embodimentsdescribed herein.

FIG. 22 is a schematic diagram of a robot with an RFID-enabled pressuresensor glove in accordance with one or more embodiments describedherein.

FIGS. 23a-23c depict alternate embodiments each representative of afinger on the RFID-enabled pressure sensor glove of FIGS. 20-22.

FIG. 24 is a diagram of an RFID tag in accordance with one or moreembodiments described herein.

FIG. 25 is a diagram of components of another embodiment describedherein.

FIG. 26 is a diagram of the proper placement of the components depictedin FIG. 25.

FIG. 27 illustrates the embodiments of FIGS. 24-26 combined with ascreen shot of software displaying the results of a test of a prototype.

FIG. 28 depicts a ring sensor that may be used in various embodimentsdescribed herein.

FIG. 29a depicts a ring sensor positioned to couple with a sourceelement in accordance with one or more embodiments described herein.

FIG. 29b depicts a ring sensor, which may be used in one or moreembodiments described herein, positioned so as to not couple with thesource element.

FIGS. 30a and 30b depict a ring sensor used as a sensor to detectwhether a hinged door is in an open or closed position in accordancewith one or more embodiments described herein.

FIGS. 31a and 31b depict a ring sensor, which may be used in one or moreembodiments described herein, configured to be used as a switch.

While the appended claims are subject to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and the accompanying detailed description. Itshould be understood, however, that the drawings and detaileddescription are not intended to limit the appended claims to theparticular embodiments described herein. This description and disclosureis instead intended to cover all modifications, equivalents, andalternatives falling within the scope of the present invention asdefined by the appended claims.

V. DETAILED DESCRIPTION

The drawings are not necessarily to scale and certain features may beshown exaggerated in scale or in somewhat generalized or schematic formin the interest of clarity and conciseness. In the description whichfollows, like parts may be marked throughout the specification anddrawings with the same reference numerals. The foregoing detaileddescription is provided for a more complete understanding of theaccompanying drawings. It should be understood, however, that theembodiments described herein are not limited to the precise arrangementsand configurations shown. Although the design and use of one or moreembodiments are discussed in detail below, it should be appreciated thatthe present description provides many inventive concepts that may beembodied in a wide variety of contexts. The specific aspects andembodiments discussed herein are merely illustrative of ways to make anduse the embodiments described, and do not limit the scope of theappended claims. It would be impossible or impractical to include all ofthe possible embodiments and contexts of the appended claims in thisdescription. Upon reading this description, alternative embodimentswithin the scope of the appended claims will be apparent to persons ofordinary skill in the art.

FIG. 1 depicts one or more embodiments described herein comprising twoor more RFID field sensors 100, a collector 110, a coupling 120, and anenclosure 130 comprising an enclosing surface or volume 125 defining aresonator (such as a waveguide or a cavity, as depicted in FIG. 1) orother enclosure 130. The collector 110 funnels, via the coupling 120,electromagnetic energy creating an electromagnetic field 135 into theenclosure 130. The electromagnetic field 135 is distributed throughoutthe enclosure 130 according to Maxwell's equations. The distribution ofthe electromagnetic field 135 within the enclosure 130 may be affectedby one or more conditions referred to herein as influences 140. Theinfluences 140 may be connected to substances such as materials orliquids within the enclosure. The RFID field sensors 100 are within andpreferably distributed throughout the enclosure 130. An RFID referencesensor 115 is typically located within or adjacent to the collector 110.

Continuing to refer to FIG. 1, an interrogator 145 sends an incidentsignal 150, to the collector 110, which, as described above, generatesthe electromagnetic field 135 within the enclosure 130. The RFID fieldsensors 100 and/or the RFID reference sensor 115, each having their ownidentification information, respond to the electromagnetic field 135 bysending reflected signals 155 with the identification of the respondingRFID field sensor 100 or RID reference sensor 115, to the interrogator145 via the coupling 120 and collector 110. The incident signal 150 andreflected signals 155 comprise radio frequency (RF) signals. Theinterrogator 145 measures returned signal strength indications (“RSSI”)of the reflected signals 155, the RSSI measurements preferably includingthe strength and the phase of the reflected signals 155. A processor(not separately depicted in FIG. 1) residing in, or connected to, theinterrogator 145 determines the characteristics of the influences 140based on the reflected signals 155 from the one or more RFID fieldsensors 100 and/or the RFID reference sensor 115. Measurements of thereflected signal 155 from the RFID reference sensor 115 may be comparedto measurements of the reflected signals 155 from the responding RFIDfield sensors 100 to identify and remove extraneous variations notrelated to the influences on the electromagnetic field.

In alternate embodiments, measurements of the electromagnetic field 135may be made by the RFID field sensors 100 and reference sensor 115 andtransmitted to the interrogator.

Although the cross-section of the enclosing surface 125 in FIG. 1 isdepicted as a rectangle or box, the enclosing surface 125 may be of anyshape convenient to the application. Although RF signals described aboveare commonly transmitted at 900 MHz UHF, different frequency bands maybe used with the embodiments described herein. The RFID sensors 100, 115used may be for example RFID integrated circuit sensors, SurfaceAcoustic Wave (SAW) RFID sensors or any other RFID sensor suitable forthe purpose.

FIG. 2 depicts one or more embodiments of the present disclosuredescribed herein in which the collector comprises a lid antenna 200 on acylindrical enclosure 210, which defines a cavity 215 (or waveguide) andwhich is at least partially filled with fill material 220 to a filllevel 222. The amount of fill material 220 and corresponding fill level222 may vary over time. An interrogator 230 sends an incident signal(not depicted) to a coupler (not depicted in FIG. 2) which transfers theincident signal into the cavity 215 so as to establish anelectromagnetic field distribution therein. The coupler might comprise,for example, an aperture shared between the lid antenna 200 and thecavity 215, or the coupler might comprise a probe from the lid antenna200 that protrudes into the cavity 215.

Continuing to refer to FIG. 2, one or more RFID field sensors 225 havingidentification information are positioned within the enclosure 210. EachRFID field sensor 225 may be, for example, an RFID integrated circuit, aSAW RFID or any other suitable RFID sensor. The RFID field sensors 225that respond to the electromagnetic field send their identificationinformation in reflected signals to the interrogator 230 via the lidantenna 200. The fill material 220 and fill level 222 compriseinfluences affecting the electromagnetic field. The interrogator 230receives the reflected signals, measures the RSSI of the reflectedsignals, and sends the RSSI measurements with the correspondingidentification of the responding RFID field sensors 225 to a processor235, which may be within or connected to or otherwise in communicationwith the interrogator 230. The processor 235 determines the type of fillmaterial and/or the fill level based on the information received fromthe interrogator 230. In FIG. 2, the processor 235 is depicted withinthe interrogator 230, but the processor 235 and interrogator 230 couldbe separate and in communication with each other. One or more referenceRFID field sensors (not depicted in FIG. 2) may be disposed on theexterior of the enclosure 210 or on or within the lid antenna 200.

In an alternative embodiment, the RFID field sensors 225 measure orestimate the received power and/or phase of the electromagnetic fieldand transmit the measurements to the interrogator 230, along with thecorresponding identification numbers of the responding RFID fieldsensors 225.

For embodiments of the present disclosure in which the enclosure 210forms a hollow waveguide or cavity, propagation of the electromagneticfield down the cavity or waveguide depends on wavelength, so the cavityor waveguide may need to be of a sufficient size such that the signal isabove a “cutoff” frequency. In one or more embodiments, the cavity orwaveguide is below cutoff when empty but is above cutoff during thepresence of an influence. For example, the dielectric property of a fillmaterial can shift the waveguide cutoff frequency below the RFIDoperating frequency to enable one or more RFID field sensors. In otherembodiments, metamaterials are employed in the cavity or waveguide tolower the cutoff frequency as an alternative to increasing the waveguideor cavity size. In other embodiments, a second conductor, such as aninner conductor, which may be in a coaxial configuration or offset, isused so as to avoid size restrictions and the associated cutofffrequency. In embodiments of the present disclosure having an outerconductor and an inner conductor, the electromagnetic field will begenerated between the outer conductor and the inner conductor. In such aconfiguration, the waveguide is capable of propagating a wave that issubstantially transverse electromagnetic (TEM). Transverse waves arewaves where the disturbance is perpendicular to the direction ofpropagation. If one throws a stone into a lake, a transverse wave iscreated: the waves move outward from the point the stone entered thewater, but to create the “wave,” the water in the lake moves up anddown. In TEM waves, the electric and magnetic field disturbances areperpendicular both to each other and to the direction of the propagationof the wave. The outer conductor and the inner conductor may havevarious shapes and/or cross sections. The inner conductor may becentered within the outer conductor or may be offset.

FIG. 3 depicts an exploded diagram of one or more embodiments of anRFID-enabled information collection system comprising a thintransmission line 300 attached to a non-conductive enclosure 315, withone or more RFID tags such as RFID integrated circuit chips 310 attachedin parallel fashion along the transmission line 300. An antenna 320attached to the enclosure 315 serves as the collector. The antenna 320is connected to the transmission line 300. An interrogator 340 sends anincident signal to the antenna 320, which launches an electromagneticfield along the transmission line 300. Similar to conventional RFIDtags, the thin RFID transmission line 300 can be printed on a thin,flexible plastic layer that attaches to the inside or outside of theenclosure 315 with an adhesive.

In the embodiment depicted in FIG. 3, the enclosure 315 is nonconductiveand sufficiently thin-walled, such that the electromagnetic field alongthe transmission line 300 is influenced by fill material 330 and itsfill level 325 inside the enclosure 315. Each RFID integrated circuitchip 310 responding to the electromagnetic field sends itsidentification with a reflected signal to the interrogator 340, whichmeasures the RSSI, such as the strength and or phase of the reflectedsignals. In alternative embodiments, the RFID integrated circuit chips310 on the transmission line 300 may measure the power of theelectromagnetic field and transmit the measurements of electromagneticfield, along with the identification of each RFID integrated circuitchip 310 performing the measurement, to the interrogator 340.

The interrogator 340 includes or is connected to a processor 345, whichuses the RSSI measurements with algorithms running on the processor 345to determine the fill level 325, distribution, permittivity, orconductivity of one or more fill materials 330 in the enclosure 315. Thealgorithms can be determined by empirical methods, by modeling, or bysolving the inverse problem, a process known to those skilled in the artin which the field solutions are determined based on an estimate of thefill level 325 and/or material, the results are compared to the measuredresults, and a nonlinear global optimizer is used to refine the bestestimate of the fill level and/or material in order to minimize thedifference between the measured response and the simulated response.

In one or more embodiments, the fill material 330 may be a liquid thateffectively shorts the transmission line 300, thus prohibiting responsefrom one or more of the RFID integrated circuit chips 310 that arepositioned below the fill level 325.

If the fill material 330 comprises one of two or more similar substanceswith similar electrical properties, such as cornflakes and oatmeal, theprocessor 345 may be able to tell the fill level but not distinguishbetween the similar substances. If the substances are different, such asliquid versus oatmeal or gravel versus oatmeal, the processor 345 may beable to distinguish the type of material 330 as well as the fill level325 and/or volume.

FIG. 4 depicts a schematic diagram of another embodiment describedherein in which a cavity 405, at least partially filled with foam 400,is formed within a conductive fabric boundary 410. A fabric antenna 420on the outside of the conductive fabric boundary 410 functions as acollector. An interrogator 430 sends an incident signal (not depicted inFIG. 4) to an antenna 420, generating an electromagnetic field in thecavity 405 with a coupling in the form of a cavity feed probe oraperture (not depicted in FIG. 4). The interrogator 430 receivesreflected signals (not depicted in FIG. 4) containing identificationinformation from one or more RFID integrated circuits 435 positionedwithin the cavity 405 and responding to the electromagnetic field. Oneor more depressions 445 in the cavity 405 acts as an influence on theelectromagnetic field. The interrogator 430 measures the RSSI of thereflected signals and sends the RSSI measurements and the correspondingidentification of the RFID) integrated circuits 435 to a processor 440,within or in communication with the interrogator 430. The processor 440may analyze information received from the interrogator 430 to deduce thelocation, or locations, at which the cavity 405 has the depressions 445.

In an alternate embodiment of the system of FIG. 4, the RFID integratedcircuits 435, as they respond to the electromagnetic field in the cavity405, measure the electromagnetic field strength and/or phase and sendthe measurements with their corresponding identification in response tothe interrogator 430.

In yet another alternate embodiment of the present disclosure depictedin FIG. 4, a conductive layer 402 is formed by a conductive paint on theboundary 410, which comprises an inflatable structure. The conductivelayer 402 of paint is continuous and contiguous for many applications,but some embodiments might allow for use of patterns of conductivepaint. Fill material within the cavity 405 created by the inflatablestructure comprises one or more gases. The temperature and pressure ofthe gas or gases exert an influence on the flexible conductive boundary410 of the cavity 405 and thus affect an electromagnetic fielddistribution (not specifically depicted in FIG. 4 but represented ingeneral previously as electromagnetic field 135 in FIG. 1) within thecavity 405, the electromagnetic field being generated by the antenna 420in response to a signal from the interrogator. RFID integrated circuits435 within the cavity 405 respond to the electromagnetic field andtransmit the identification of the responding RFID integrated circuit(s)435 in reflected signals to the interrogator 430, which measures RSSI ofthe reflected signals and sends the measurements to the processor 440.Alternatively, the strength and phase of the electromagnetic field ismeasured by the RFID integrated circuits 435, which transmit themeasurements and the specific identification of each of the respondingRFID integrated circuits 435 to the interrogator 430. The processor 440in communication with the interrogator 430 can use the informationreceived from the interrogator 430 to determine the volume of the gas orgases within the cavity 405, thus permitting solution for the pressure,assuming the temperature is known. If there is a depression 445 of theboundary 410, the depression 445 would act as an influence on theelectromagnetic field and facts about the extent of the depression 445could be determined by the processor 440 in analyzing the informationreceived from the interrogator 430.

FIG. 5 depicts one or more embodiments of the present disclosure inwhich a conductive, flexible diaphragm 510 applies pressure to andreduces the volume of a conductive cavity 520, resulting in changes inan electromagnetic field (not depicted) within the cavity 520. Anantenna (not depicted in FIG. 5) which receives an incident signal froman interrogator 535 and couples electromagnetic energy to the cavity520, creating the electromagnetic field within the cavity 520. Theelectromagnetic field distribution within the cavity 520 is sensed byone or more RFID field sensors 530 within the cavity 520. The RFID fieldsensors 530 may respond with reflected signals, including identificationof the responding RFID field sensors 530 to the interrogator 535. Theinterrogator 535 measures the RSSI of the reflected signals and sendsthe measurements and the corresponding identification of the respondingRFID field sensors 530 as information to a processor 540, within orconnected to the interrogator 535. The processor 540 uses theinformation to determine the pressure applied by the diaphragm 510. Theprocessor 540 in FIG. 5 is depicted as being within the interrogator535, but the processor 540 could also be in communication with theinterrogator without being within the interrogator 535.

In an alternate variation of the embodiment of FIG. 5, the cavity widthis designed to render the cavity 520 close to the cutoff frequency onthat dimension. The degree to which the diaphragm 510 is depresseddetermines how far below cutoff the antenna is as a function offrequency. The interrogator 535 may communicate over a number ofchannels, each channel distinguished by a range of frequencies. Theinterrogator 535 may hop between alternative channels using afrequency-hopping spread spectrum technique, as is well known in theart. An RSSI associated with each RFID field sensor 530 is reported forthe various frequencies used by the interrogator 535, thus providinginformation from which the extent and location of the volume reductionof the cavity 520 can be estimated.

FIG. 6 will be discussed in more detail with FIG. 10 below.

Referring now to FIG. 7, an enclosure in the form of a container ordispenser 710, with a quantity of N embedded RFID tags 720, enablessensing of fill material 725 and fill level 730. The container ordispenser 710 has an inner conductor 715 and conductive container walls705. (The inner conductor in FIG. 7 is depicted as coaxial, but in otherembodiments, the inner conductor may be offset. The enclosure and innerconductor may have a variety of cross sectional shapes, such ascircular, triangular, rectangular, trapezoidal, or any otherpolygonal-shape.) A lid antenna 735 serves as a coupling and, stimulatedby an incident signal from an interrogator 745, excites a coaxialwaveguide formed by the container 710 and inner conductor 715 andgenerates an electromagnetic wave (not specifically depicted in FIG. 7).The electromagnetic wave travels down the waveguide and provides powerto the quantity N RFID tags 720. The powered RFID tags 720 respond bytransmitting their identification to the interrogator 745, whichmeasures the RSSI and provides information comprising the RSSImeasurements and the corresponding identification of the responding RFIDtags to a processor 740, within or connected to the interrogator 745.The processor 740 may be configured to use the information received fromthe interrogator 745 to determine facts regarding the fill material 725and fill level 730. Preferably, a reference RFID tag (not depicted inFIG. 7) resides on top of or within the lid antenna 735, or is placedsomewhere on the exterior of the container 710. The reference signalstrength is compared with that from the other responding RFID tags 720within the waveguide in order to remove variations due to the exteriorpropagation channel between the interrogator 745 and the lid antenna735. Although the bottom of the container or dispenser 710 (opposite thelid) presents a short circuit of the coaxial structure in the embodimentdepicted in FIG. 7, in general, a matched or other suitable load can beused to terminate the waveguide. Material can be removed through the lidantenna 735 or, alternatively, from a dispensing mechanism (not shown).Alternatively, the lid and antenna can be on opposing ends of thecontainer or dispenser 710.

FIG. 8a is a diagram of an exterior of a prototype of another embodimentdescribed herein. In FIG. 8a , a reference RFID tag 800 is fastened tothe top of a container lid antenna 810, which may comprise acapacitively-fed planar inverted F antenna (“PIFA”). A container wall820 also serves as the outer conductor of a coaxial waveguide in FIG. 8a. An inner conductor (not shown in FIG. 8a ) protrudes through the lid810, with isolation to prevent shorting to the lid 810, and makescontact with a capacitive feed plate (not visible in FIG. 8a ). Thecontainer is filled with oatmeal, an example of a fill material. Aninterrogator (not visible in FIG. 8a ) sends an incident signal to thecontainer lid antenna 810, which generates an electromagnetic field. Oneor more field RFID tags (not depicted in FIG. 8a ), each havingidentification information, are placed on the internal side (not visiblein FIG. 8a ) of the container outer conductive wall. The field RFID tagsand the reference RFID tag 800 respond to the electromagnetic field,transmitting their identifications via the container lid antenna 810 tothe interrogator. The interrogator measures the RSSI of thetransmissions from the responding RFID tags and sends informationincluding the measurements and the identification of the correspondingresponding RFID tags for recordation and analysis by a processor (notvisible in FIG. 8a ) within or in communication with the interrogator.The processor uses the recorded information to determine the quantity ofoatmeal within the container 820. Measurements of responses from theRFID reference tag 800 may be compared to measurements of responses fromthe responding field RFID tags to identify and remove extraneousvariations not related to the influences on the electromagnetic field.

) FIGS. 8b, 8c, 8d and 8e are diagrams showing additional details of acapacitively-fed planar inverted F antenna (“PIFA”), such as the antenna810, which could be used with embodiments described herein similar tothe one pictured in FIG. 8a . As depicted in FIG. 8b , which provides aside view of the lid antenna, the lid antenna 810 b comprises a topplate 812, a capacitive feed plate 813, and a ground plate 814, with ashorting strip 818 connecting the top plate 812 to the ground plate 814.A feed post 815 attached to the capacitive feed plate 813 passes throughan opening in the ground plate 814 and extends into the cavity ofcontainer 820 e. The feed post 815 is provided with an insulatingstandoff 816 from the body of the antenna 810 b at a clearance 817. FIG.8c provides a top view of the lid antenna 810 b, the top plate 812 andthe shorting strip 818.

FIG. 8d and FIG. 8e depict a patch lid antenna 810 d for a coaxial feedto an embodiment of the present disclosure comprising an RFID-enabledcontainer 820 e with conductive walls 822 e. FIG. 8d depicts a patch lidantenna 810 d with top and bottom layers 811 d and a feed post 815 d(which may also be called a “center post”). Optional threads 823 may beused to couple the lid antenna 810 d to the container 820 e. As depictedin FIG. 8e , within the container 820 e, the feed post 815 d may bereceived by an insulating center post guide 824 e terminating in aconductive termination pad 825 e.

FIG. 9 depicts a graph of results of four different trials using theprototype of FIG. 8a . As discussed above, for each trial, when theinterrogator sends an incident signal to the container lid antenna 810,the container lid antenna 810 receives an electromagnetic field. Theinterrogator measures RSSI from signals sent by RFID tag I and thereference tag and sends the measurements and identification of thecorresponding RFID tags 800 to the processor. For each trial, thecontainer 820 is removed from its position near the interrogator,emptied, and then filled with oatmeal to the level indicated on theX-axis and a new trial is run. For this prototype, no attempt was madeto maximize the power passed from the container lid antenna 810 to thecontainer 820, nor was any attempt made to equalize the sensitivity fordifferent depths of fill material. Note how the trial lines varysomewhat at lower levels of cups of oatmeal, but the trial plotsconverge more closely as the cups of oatmeal increase. This convergenceindicates that in these tests, this particular prototype is moreaccurate for higher fill levels than for lower level fills. However, theprototype serves the purpose of monitoring the fill level of a container820 or dispenser. No batteries are required, and a single interrogatormay remotely monitor a wide angular span of different containers ordispensers.

The embodiments described herein permit moderate to very fine resolutionRFID tracking. A pill dispenser is an example of an application thatwould require fine resolution RFID tracking. Pills are typically toosmall for secure attachment of conventional RFID tags. In addition,accidental ingestion of RFID tags might not be beneficial for thepatient. Furthermore, the tag cost would likely be prohibitive forattachment at the pill level.

Referring now to FIG. 10, a schematic of a conventional dispenser, suchas a pill dispenser, is shown. The items 1000 to be dispensed, which maybe pills or other small items, from a dispenser 1005 are placed on topof or adjacent to a traveler 1010, which compresses a spring 1020. Items1000 can be removed by a plunger 1025 which pushes one of the items 1000through an opening 1030. Spring tension in the compressed spring 1020pushes the traveler 1010 and items 1000 forward to fill the vacatedslot.

FIG. 6 is a schematic diagram depicting an RFID-enabled dispenser 600that would be placed in a holder (not depicted in FIG. 6) having one ormore cells (not depicted in FIG. 6). The RFID-enabled dispenser of FIG.6 could be used as part of embodiments of the present disclosure likethose depicted in FIGS. 11-19 herein, which are discussed in more detailbelow. The dispenser 600 may have a cylindrical structure 609, with acircular cross-section 605. A traveler 620 positioned by a spring 642moves items 602, which can be pushed by a plunger 644 (acting through afirst opening 638) through second opening 640. The items 602 mightcomprise disks containing one or more individual objects 613. The disc602 depicted in the inset of FIG. 6 is segmented in a pie fashion, withan object 613 in each segment, but the item 602 may comprise any kind ofconvenient or desired type of packaging and may have shapes other thanthat of a disc. Items comprising a package containing a plurality ofobjects may be used with various embodiments of the RFID-enabled itemdispenser of the present disclosure.

FIG. 11 is an exploded view of a modified version of the dispenser ofFIG. 10, wherein additional components are included to create anembodiment of the present disclosure, an RFID-enabled dispenser. As inFIG. 10, the items 1000 to be dispensed are placed on top of or adjacentto a traveler 1130, which compresses a spring 1120. But the RFID-enableddispenser 1102 of FIG. 11 has additional components which include acollector 1100, such as an antenna, conductive layers 1105 to form awaveguide, such as a parallel plate waveguide 1110 (the parallel platesof the parallel plate waveguide comprising the conductive layers 1105),and one or more RFID sensors 1115. The RFID sensors 1115 are positionedon one or both sides of the parallel plate waveguide 1110 such that theends establish electrical connection to the waveguide conductive layers1105. The conductive layers 1105 are typically solid but specializedapplications may permit the use of patterned conductive layers. The RFIDsensors 1115 could be placed intermittently or periodically along theaxial direction of the waveguide 1110. An interrogator, not depicted inFIG. 11, sends an incident signal to the collector 1100, creating anelectromagnetic field in the waveguide 1110. The RFID sensors 1115 mayrespond to the electromagnetic field and send information includingtheir identification as reflected signals to the interrogator. Theinterrogator measures the RSSI of the reflected signals and transmitsinformation comprising the measurements and corresponding RFID sensoridentification to a processor within or in communication with theinterrogator. The processor records and/or analyzes the informationreceived from the interrogator and may determine data concerning theitems 1000 to be dispensed, such as the number of items alreadydispensed and/or the number of items remaining in the dispenser 1102 andpossibly the type or material of the items 1000. A first opening 1122 inone waveguide plate permits a plunger 1125 to move forward, and a secondopening 1124 in the opposing waveguide plate permits items 1000 to bedispensed. Both the first opening 1122 and the second opening 1124 aresufficiently small to not disrupt continuity of the conductive waveguide1110. Alternatively, the first and second openings 1122, 1124 may belocated on the two sides orthogonal to the conductive waveguide plates,in which case an RFID sensor 1115 would be positioned so as not tointerfere with the plunger 1125 or block the dispenser opening. As analternative to a plunger 1125, other dispensing mechanisms could be usedto dispense items from the dispenser 1102.

In a variation of the embodiment of FIG. 11, the traveler 1130 may bemodified from a conventional form to have one or more conductivesurfaces, or to be predominantly conductive, so as to present anelectromagnetic short to the waveguide 1110. The position of themodified traveler 1130, and hence the short, affects the wave pattern ofthe electromagnetic field and hence the RSSI, and possibly phasemeasurements, from each of the one or more RFID sensors 1115. Forexample, the one or more conductive surfaces could short one of theadjacent RFID sensors 1115. Alternatively, the one or more conductivesurfaces could enable one of the RFID sensors 1115 by establishing theproper impedance presented by the RFID sensor 1115 to the waveguide. Theprocessor, upon receiving the information from the interrogator,determines the quantity of the items 1000 remaining in the RFID-enableddispenser 1102, and possibly the type or material of the items 1000.

In another version of the embodiment of FIG. 11, an RFID sensor 1115 isembedded into the traveler 1130 such that the traveler 1130 absorbsincident energy from the incident signal, providing a different type ofload to the waveguide 1110 and an RSSI value (and possibly phase)corresponding to the terminal end of the waveguide 1110. The position ofthe traveler 1130 would be determined from RSSI measurements made by theinterrogator from signals carrying identification information sent bythe responding RFID sensors 1115 to the interrogator. (Alternatively, insome embodiments, the RFID sensors 1115 may measure an electromagneticfield created by the configuration of the embodiment and transmit theRSSI measurements to the interrogator.) In another embodiment, thetraveler 1130 is designed to present a predetermined, but arbitrary,electromagnetic load.

FIG. 12 depicts one or more embodiments of the present disclosure in theform of a dispenser 1202 in which the collector 1200 provides an inputsignal to a spring end of the waveguide 1210 (on the opposite sidecompared to FIG. 11). The waveguide of FIG. 12 is a type of coaxialwaveguide 1210 with the spring 1220 serving as a center conductor andexerting a force to traveler 1230.

In a variation of the embodiment of FIG. 12, the surrounding structureconstitutes a parallel plate waveguide, while in another version thestructure constitutes a fully enclosed conductive cylinder 1205, ofarbitrary shaped cross-section. For the parallel plate embodiment, oneor more RFID sensors (not depicted in FIG. 12) having individualidentification information would be positioned along one or both gapsbetween the parallel plates. For the fully enclosed cylinder embodiment,the RFID sensors would be positioned in the internal volume or at theentry/exit plane of the waveguide.

In each version of the embodiment of FIG. 12, an interrogator (notdepicted) sends an incident signal to the collector 1200, whichgenerates an electromagnetic field. The RFID sensors which respond tothe electromagnetic field send their identification information via thecollector 1200 to the interrogator, which measures the RSSI and sendsthe measurements and corresponding identification information to aprocessor, within or in communication with the interrogator, foranalysis. (Alternatively, the RFID sensors make measurements of theelectromagnetic field and send the measurements and the responding RFIDsensors' identification as reflected signals via the collector 1200 tothe interrogator.) The processor uses the measurements and sensoridentification information to determine the amount or type of itemswithin the dispenser and/or the number of items which have beendispensed.

FIG. 13 depicts a cross-section of a fine resolution RFID dispenserassembly 1300 in accordance with another embodiment described herein. InFIG. 13, a dispenser 1302, with items 1325 to be dispensed within, isplaced within a holder 1305, which comprises an elongated structure withmultiple holder cells 1310, each holder cell 1310 containing an RFIDcircuit 1315 with an individual identification. The holder cells maycomprise but are not limited to parallel plate cells. A plunger 1335,acting through a first opening 1338, pushes an item 1325 to be dispensedthrough a second opening 1340. A traveler 1320 contains a dielectricbody 1330 within and is connected to a spring 1345, operating similarlyas in FIGS. 11 and 12. The position of the traveler 1320 is determinedby the number of items 1325 remaining within the dispenser 1300. Theposition of the traveler 1320 and its dielectric body 1330 enables oneof the RFID holder cells 1316 to be energized in that it receivessignals from an interrogator (not depicted) and responds to the signals.The interrogator and a processor within or in communication with theinterrogator, upon receiving the unique ID code of the responding RFIDcircuit in the energized RFID holder cell 1316, are able to deduce thenumber of items 1325 remaining within the dispenser. (In alternateembodiments, all holder cells except one could be energized by anappropriate design, and the number of items remaining in the dispensercould be deduced by the interrogator and an appropriately programmedprocessor by determining the identity and thus the location of thenon-responding holder cell).

Details of the holder cells of FIG. 13 are provided in FIG. 14. Eachholder cell 1310 comprises a top floor 1410 and bottom floor (notvisible in FIG. 14), each with a corresponding conductive pattern 1425,1430. The top and bottom floor conductive patterns 1425, 1430 may beidentical. The interior sections 1440 of the floors are hollow in orderto support the dispenser 1302 body (not depicted in FIG. 14).

FIG. 15 is a schematic diagram depicting a holder cell 1310 and aresulting conductive pattern 1500 from the traveler 1320 when thetraveler 1320 moves within the structure of a holder cell 1310, inaccordance with one or more embodiments described herein. Referring backto FIG. 13, note that the convergence of the dielectric body 1330 of thetraveler 1320 with the conductive patterns 1425, 1430 of the holder cell1310 energizes an RFID circuit (not depicted in FIG. 15) within theholder cell 1310.

FIG. 16 depicts one or more embodiments of an RFID enabled dispenser1600 in accordance with the present disclosure. Similar to theembodiment depicted in FIG. 13, the dispenser 1600 comprises adispensing chamber 1612, with items 1625 to be dispensed within, placedwithin a holder 1605. The holder 1605 comprises an elongated structurewith multiple holder cells 1610, each holder cell 1610 containing anRFID sensor 1615 with a unique identification. A plunger 1635 isdesigned to act through a first opening 1638 to push an item 1625 to bedispensed through a second opening 1640. A traveler 1620 contains adielectric body 1630 within and compresses a spring 1645, operatingsimilarly as in FIGS. 11-13. The position of the traveler 1620 isdetermined by the number of items 1625 remaining within the dispenser1600. Unlike FIG. 13, in FIG. 16, an electromagnetic short 1650 on oneend of the holder cells 1610 functions to reduce the physical size ofthe holder cell 1610 required for resonance, such as a quarter-wavepatch antenna or a planar inverted-F antenna (PIFA). The position of thetraveler 1620 and its dielectric body 1630 enables one of the holdercells 1610, a RFID holder cell 1616 that is energized, to function as anoperable antenna at the frequency of operation, and hence enables theRFID sensor in the energized holder cell 1616 to receive signals from aninterrogator (not depicted) and to respond to the signals. Theinterrogator and a processor within it, upon receiving the unique IDcode of the responding RFID sensors 1615, are able to deduce the numberof items 1625 remaining within the dispenser 1600.

FIG. 17 depicts one or more embodiments of an RFID enabled dispenser1700 in accordance with the present disclosure. In structure andoperation, the embodiment in FIG. 17 is similar to that of FIGS. 13 and16. The dispenser assembly 1700 includes a dispensing chamber 1712, withitems 1725 to be dispensed, placed within a holder 1705. The holder 1705comprises an elongated structure with multiple holder cells 1710, eachholder cell containing an RFID sensor 1715 with a unique identification.A plunger 1735 is designed to act through a first opening 1738 to pushan item 1725 to be dispensed through a second opening 1740. A traveler1720 contains a dielectric body 1730 within and compresses a spring1745, operating similarly as in FIGS. 11-13 and 16. The position of thetraveler 1720 is determined by the number of items 1725 remaining withinthe dispenser 1700. As with the embodiment of FIG. 16, anelectromagnetic short 1750 on one end of the holder cells 1710 functionsto reduce the physical size of the holder cell 1710 required forresonance, such as a quarter-wave patch antenna or a planar inverted-Fantenna (PIFA). The position of the traveler 1720 and its dielectricbody 1730 enables one of the holder cells 1710 to function as anoperable antenna at the frequency of operation, and hence enables theRFID sensor in the energized cell to receive signals from aninterrogator (not depicted) and to respond to the signals. In theembodiment of FIG. 17, the dispensing chamber 1712 of the RFID enableddispenser 1700 is separable from the holder 1705, as depicted.

FIG. 18 illustrates another embodiment in which a remote RFID reader(also called an interrogator) 1800 interrogates an RFID-enableddispenser 1805, and only a single active RFID holder cell 1810,determined by a traveler 1815 position, responds. A holder 1820comprises a collection of holder cells 1825, each of which may compriseany of a number of types of antennas, including but not limited tohalf-wave microstrip patches, quarter-wave patches, and PIFAs. Eachholder cell 1825 contains an RFID sensor 1830. When the traveler 1815,positioned by a spring 1816, moves to the location of the representativeholder cell 1810, that holder cell 1810 is energized, that is, suitablytuned or enabled as an antenna to receive energy from the interrogator1800, transfer energy to the particular RFID sensor 1812 operativelyconnected to the energized holder cell 1810, and re-radiate energy fromthe RFID sensor 1812 to the interrogator 1800. When the traveler 1815 isnot positioned within the location of the holder cell 1810, holder cell1810 is not conducive to transferring energy from the collector means tothe RFID sensor 1812 associated with this particular holder cell. Whenthe traveler 1815 is within the location of the holder cell 1810, thisparticular holder cell 1810 activates and sends signals back to theinterrogator 1800 for analysis by a processor (not separately depictedin FIG. 18) within or in communication with the interrogator 1800. Basedon the RFID sensor 1812 that responds, the processor can determine theposition of the traveler 1815 and hence the quantity of items 1835remaining within the dispenser 1805 (or the quantity of items which havebeen dispensed). As with the embodiments of FIGS. 13 and 16, a plunger1845 acts through a first opening 1838 to push an item to be dispensedthrough a second opening 1840.

To augment the effect of the traveler 1815 residing within the holdercell 1810; i.e. to enhance the ability of the energized holder cell 1810to couple energy to the RFID sensor 1812 that shares the same holdercell 1810 as the traveler 1815, the structural body of traveler 1815might include an enhanced coupler. Examples of possible enhancedcouplers include but are not limited to a high dielectric body thattunes (1) the resonant frequency of the holder cell 1810 so as to befunctioning as an antenna; (2) the impedance of the holder cell 1810 tomatch that of a collector; or (3) the resonance of the energized holdercell 1810 to affect the cavity impedance response of the holder cell1810. In another embodiment, the traveler 1815 might comprise a topconductive pattern and a bottom conductive pattern with an insulator inthe middle. In yet another embodiment, the traveler 1815 might comprisea short between the top and bottom conductive patterns, in which theshort tunes the holder cell 1810 as the traveler 1815 enters.

Communication protocols organize exchanges of information betweendevices. The response of the RFID sensors within the holder cellsfunctioning as an antenna of FIG. 18 may follow such a communicationprotocol, with the interrogator also following the same protocol. Onesuch protocol is the EPCglobal Class 1 Generation 2 protocol.

FIG. 19a is a combined front and side view of another embodimentdescribed herein in which an RFID-enabled item dispenser 1900 dispensesitems 1902. A first half 1906 of conductive cell patterns are formed ona first printed circuit board (a first PCB) 1905 and a second half 1908of the conductive cell patterns are formed on an opposing (or “back”)side (a second PCB) 1910 with a dispenser unit 1915 between the firstand second PCBs 1905, 1910. Similar to previous embodiments describedabove, a traveler 1920 enables communications to and from an RFIDcircuit (not depicted in FIG. 19a ) within a particular cell 1931 of theholder cells 1930 formed by the first and second halves of theconductive patterns 1906, 1908. A top conductive pattern 1935 on thetraveler 1920, possibly in conjunction with a dielectric body, enablesthe particular cell 1931 hosting the traveler 1920 to receive and sendRFID signals from/to the interrogator. (As the traveler changesposition, other holder cells would become activated.)

Continuing to refer to FIG. 19a , the conductive patterns 1906, 1908 onthe first and second PCB's 1905, 1910 might be different; e.g., thefirst half of the conductive pattern 1906, on the first PCB, might becharacterized with one or more empty regions, whereas the second half1908 of the conductive pattern, on the second PCB 1910, might be asingle filled conductive region. In other embodiments, the conductivepatterns 1906, 1908 might be identical.

FIG. 19a also depicts a dispenser door 1940 at the base of the dispenser1900. Although other embodiments discussed herein have indicated aspring that presents a force to propel the traveler 1920, othermechanisms (called “forcing elements” herein) might be used to propelthe traveler 1920, such as (but not limited to) gravity (as depicted inFIG. 19a ), levers, masses placed above the traveler 1920 in thepresence of gravity, or gears.

In a variation of the embodiment depicted in FIG. 19a , the second PCB1910 does not contain the second half of the conductive pattern 1908.Instead, an additional conductive pattern is placed on the back side ofthe traveler 1920. In various embodiments, the traveler may have aconductive pattern on one side and solid metal on the other or thetraveler may have solid metal on one side and a dielectric on the otheror both sides of the traveler may have conductive patterns. In one ormore embodiments of the present disclosure, the traveler may have a sidewith a solid metal and one of the PCB's may have a continuous groundplane. When the traveler rests in a holder cell functioning as anantenna, the traveler shorts out the holder cell, deactivating it andits operation as an antenna. As other holder cells are activated, thelocation of the de-activated holder cell provides the location of thetraveler and thus discloses the number of items contained in thedispenser.

FIG. 19b is a schematic diagram depicting one or more embodiments of thepresent disclosure in the form of an RFID-enabled item dispenser 1900 bin which a top conductive layer 1906 b comprises one or more ringmicrostrip antenna circuits 1901 b, each of which is attached to an RFIDsensor 1915 b. As the terms are used with respect to FIGS. 19a-19f , a“conductive layer” is not necessarily a solid conductive layer. The topconductive layer 1906 b is conductive in the sense that it includes thering microstrip antenna circuits or other antenna pattern; it does nothave to be a solid conductive layer. The ring microstrip antennacircuits 1901 b may be rectangular, as depicted in FIG. 19b , circular,triangular or have some other configuration. The top conductive layer1906 b is attached to a dielectric layer 1907 b. A traveler conductivelayer 1935 b is parallel and adjacent to the dielectric layer 1907 b.When adjacent to one of the ring antenna circuits 1916 b, the travelerconductive layer 1935 b enables the adjacent ring microstrip antennacircuit 1916 b, with its RFID sensor, to send and receive signals to andfrom an interrogator (not depicted in FIG. 19b ) within a frequency bandof operation. The traveler 1920 b in FIG. 19b is propelled by a spring1942 b, although other forcing elements might be used. As with similarembodiments of an RFID-enabled dispenser discussed herein, in FIG. 19b ,a plunger 1944 b, acting through a first opening 1938 b, pushes the item1902 b to be dispensed through a second opening 1940 b.

FIG. 19c depicts another embodiment of an RFID-enabled item dispenser1900 c, in accordance with one or more embodiments described herein. TheRFID-enabled item dispenser 1900 c is otherwise similar to theembodiment depicted in FIG. 19b , but in which a traveler conductivelayer 1935 c is inserted between the body of the traveler 1920 c and atraveler dielectric layer 1936 c. Similar to FIG. 19b , in FIG. 19c , aring microstrip conductive layer 1906 c overlays a dielectric layer 1907c on the dispenser. The ring microstrip conductive layer 1906 c formsmicrostrip ring antenna cells 1901 c, each having an RFID sensor 1915 c.The conductive layer 1906 c may be outside the dielectric layer 1907 cas depicted in FIG. 19c or inside the dielectric layer 1907 c (not shownin FIG. 19c but as depicted in FIG. 19d with similar parts 1906 d(conductive layer) and 1945 d (dielectric or insulating layer)). Similarto other embodiments discussed herein, a plunger 1944 c may act througha first opening 1938 c to propel items 1902 c through a second opening1940 c. The traveler 1920 c activated by a spring 1942 c, forces theitems 1902 c upwards toward the second opening 1940 c. The position ofthe traveler 1920 c and the traveler conductive layer 1935 c activates aparticular microstrip ring antenna cell 1916 c to send and receivesignals to and from an interrogator (not depicted in FIG. 19c ) within afrequency band of operation.

FIG. 19d depicts yet another embodiment of an RFID-enabled itemdispenser 1900 d, otherwise similar to the embodiments of FIGS. 19b and19c , in which a traveler conductive surface 1935 d folded around thetraveler dielectric layer 1936 d provides a ground plane with a short ontraveler 1920 d. In FIG. 19d , an insulating layer 1945 d overlays aring microstrip conductive layer 1906 d on the dispenser. The ringmicrostrip conductive layer 1906 d forms microstrip ring antenna cells1901 d, each having an RFID sensor 1915 d. The design with the ringmicrostrip conductive layer 1906 d on the inside of the insulating layer1945 d and the traveler design may allow one to make the microstrip ringantenna cells 1901 d and the RFID-enabled item dispenser 1900 d morecompact than in other embodiments. Similar to other embodimentsdiscussed herein, a plunger 1944 d may act through a first opening 1938d to move or propel items 1902 d through a second opening 1940 d. Thetraveler 1920 d activated by a forcing element such as a spring 1942 d,propels the items 1902 d upwards toward the second opening 1940 d. Theposition of the traveler 1920 d and the traveler layers 1935 d, 1936 dactivates a particular microstrip ring antenna cell 1916 d to send andreceive signals to and from an interrogator (not depicted in FIG. 19d )within a frequency band of operation.

FIG. 19e depicts another embodiment in accordance with the presentdisclosure. An RFID-enabled dispenser 1900 e has a cylindrical structure1909 e, with a circular cross-section 1905 e and a hollow interiorregion 1903 e. A top layer of ring microstrip antennas 1901 e arewrapped around the circumference of cylindrical structure 1909 e. Thering microstrip antennas 1901 e are each attached to an RFID circuit1915 e. The cylindrical structure 1909 e optionally has an insulatinglayer 1908 e. A ground plane typically associated with ring microstripantennas 1901 e is absent in the embodiment depicted in FIG. 19e ,except as provided by a traveler 1920 e. The traveler 1920 e may have anoptional traveler dielectric layer 1937 e that surrounds a travelerconductive layer 1935 e. The traveler 1920 e is displaced due to aforcing element, such as a spring (not depicted in FIG. 19e ) or asdescribed in other embodiments described herein, when items (notdepicted in FIG. 19e ) are removed or added. The position of thetraveler 1920 e allows the traveler conductive layer 1935 e to provide aground plane to a particular microstrip antenna 1916 e, to enable theparticular microstrip antenna 1916 e and allow the RFID circuit attachedto the particular microstrip antenna 1916 e to send and receive signalsto and from an interrogator. The interrogator and a processor operate asdescribed herein with respect to other RFID-enabled item dispensers, butare not specifically shown in FIG. 19 e.

FIG. 19f is an illustration of an RFID-enabled item dispenser 1900 f inaccordance with one or more embodiments of the present disclosure inwhich a top conductive layer 1908 f of one or more microstrip antennas1901 f is wrapped around a cylinder 1909 f with circular cross-section1905 f. As in previously described embodiments, a traveler (not depictedin FIG. 19f ) provides the ground plane associated with the topconductive layer 1908 f to form a completed microstrip antenna conformalto the cylinder 1909 f. A loop 1914 f with an RFID integrated circuit1915 f is preferably placed in the gap of each antenna 1901 f asdepicted in FIG. 19f . In one embodiment, the microstrip antenna 1901 fis resonant at approximately one-half wavelength. A traveler mechanism,including the traveler, a forcing element, and a dispensing mechanismwould operate as described with respect to other embodiments describedherein but is not shown in FIG. 19 f.

FIGS. 20, 21, 22, and 23 a-c illustrate one or more embodiments of thepresent disclosure in the form of a pressure sensor glove 2005.Referring first to FIG. 20, the “palm” 2000 side of a pressure sensorglove 2005 comprises ring elements 2010 positioned on foam pads 2015.The foam pads 2015 are placed at various locations on the palm anddigits (i.e., in the areas for the fingers and the thumb), as depictedin FIG. 20, to yield desired sensitivity such that when a ring element2010 is depressed, the ring element 2010 couples to a source, such as afirst microstrip line 2115 or a second microstrip line 2120 (bothdepicted in FIG. 21). The first microstrip line 2115 would be visible inFIG. 20, but it is hidden under a layer of the glove. On the palm sideof the glove, the first microstrip line 2115 may terminate with loadelements close to the ring elements situated on the palm. An RFIDcircuit 2020 is attached to each ring element 2010. FIG. 21 depicts theother side 2100 of the glove, in other words, the back or top side ofthe glove 2005, in accordance with one or more embodiments describedherein. A microstrip patch antenna 2110 is connected to the firstmicrostrip line 2115 for coupling to the ring elements 2010 positionedon the palm and to the multiple second microstrip lines 2120 forcoupling to the ring elements 2010 positioned on the digits. A loadelement 2125 is at the end of each second microstrip line 2120. The loadelements 2125 can comprise (for example): (1) a resistive material thatabsorbs incident electromagnetic (EM) energy to prevent reflections; or(2) an RFID integrated circuit (IC) that reports received power as astatus on the health of the system and the amount of power coupled toring elements 2010. The load elements 2125 act to prevent unintendedimpedance mismatch. As depicted in FIG. 22, an interrogator 2200, suchas a robot-based interrogator, can communicate with the pressure sensorglove 2005 wirelessly, thus eliminating cable runs across joints. Aprocessor (not depicted) may be in communication with the interrogator2200 to analyze information received by the interrogator 2200.

The “glove” 2005 could take the form of an artificial hand or othergripping tool, as well as a glove that can be removed from a human ormechanical hand. Similarly, although human hands typically have fourfingers and one thumb (designed to be an opposing thumb), the glove 2005of the present disclosure may be designed with a different number ortype of digits, if it would be advantageous for a particularapplication, for example.

FIGS. 23a-23c each depict a different detailed embodiment of componentson the digits of the glove 2005 of FIGS. 20-22, with similararrangements also available for use on the palm (not shown). In FIG. 23a, a dipole antenna 2305 with direct coupling to depressed rings 2310 isused. The dipole antenna 2305 is partially disposed on the surface ofthe digit opposite to the positioning of ring elements 2310. The dipoleantenna 2305 may include meandered lines to achieve resonance. Inoperation, when one or more of the ring elements 2310 are depressed, thedepressed ring element 2310 directly couples with the dipole antenna2305. The RFID circuit 2020 on the depressed ring element 2310 iscorrespondingly energized. The RFID circuit 2020 sends information viathe dipole antenna 2305 to the interrogator 2200 and the associatedprocessor for further analysis.

Alternatively, in FIG. 23b , a top antenna 2320 is placed on top of thedigit of the glove 2005. (Note the position of the top antenna 2320relative to the load element 2125.) The top antenna 2320 may, forexample, comprise a microstrip patch or a planar inverted “F” antenna.In operation, when one or more of the ring elements 2010 are depressed,the RFID circuit 2020 on the depressed ring element 2010 (or elements)is energized. The energized RFID circuit 2020 sends a response via thetop antenna 2320 to the interrogator 2200 and the processor foranalysis.

FIG. 23c depicts another alternate embodiment wherein the antenna isremote from the digit (and thus not depicted in FIG. 23c ). In thisembodiment, the second microstrip line 2120 may be connected to theantenna or the interrogator. In operation, when one or more of the ringelements 2010 are depressed, the RFID circuit 2020 on the depressed ringelement 2010 (or elements) is energized. The energized RFID circuit 2020sends a response via the remote antenna to the interrogator 2200 and theprocessor for analysis.

) FIGS. 24-27 depict another group of embodiments of the presentdisclosure. FIG. 24 is a diagram of a prototype of one embodiment. Inthe diagram of FIG. 24, a microstrip transmission line in a loop 2400creates a circuit with an RFID sensor 2410. Collectively thetransmission line 2400, circuit and RFID sensor 2410 are called an RFIDtag 2420. The microstrip transmission line loop 2400 of FIG. 24 isprinted on a 20 mil (0.02 inch) thick piece of hydrocarbon ceramiclaminate 2415 manufactured by the Rogers Corporation and soldcommercially as RO 4350. In this prototype, the RFID sensor 2410comprises an Alien® Higgs-3 SOT sold commercially by Alien Technology ofMargan Hill, Calif. While the loop 2400 is shown as being rectangular,other shapes (square or oval for example) could also be used.

FIG. 25 is a diagram of components of a prototype of another embodimentof the present disclosure. In the diagram of FIG. 25, a 50 ohm load 2510is connected to a board structure comprising a second microstriptransmission line 2515, functioning as an operably planar openwaveguide, with an RF feed 2520 on the opposing end of the secondmicrostrip transmission line 2515. The RF feed 2520 is connected to anRFID interrogator (not shown specifically in FIG. 25 but representedgenerally in other drawings herein) for this prototype, butalternatively, an antenna could be used to receive and transmit signalsfrom and to an RFID interrogator, which may have an internal processoror may be connected to an external processor such as a laptop or desktopcomputer. The second microstrip transmission line 2515 in FIG. 25 isprinted on a second base 2530 functioning as an operatively insulatingdielectric base, such as a 175 mil thick, ceramic-filledpolytetrafluoroethylene (PTFE) composite material sold by the RogersCorporation commercially as RO 3003. The 50 ohm load 2510 preventsdevelopment of a standing wave pattern. The RFID tags 2420 of FIG. 24are placed on an operatively insulating and compressible substrate 2525,such as a one half inch thick foam block, face down. The RFID tags 2420are bonded or otherwise fastened to the substrate 2525 to form thiscomponent of the prototype.

FIG. 26 is a diagram of the proper placement of the components shown inFIG. 25. Specifically, in the diagram of FIG. 26, proper placement ofthe substrate 2525 with respect to the second transmission line 2515 isdepicted. (The second transmission line 2515 is not visible in FIG. 26or FIG. 27, but its position can be determined by the position of theload 2510 and the RF feed 2520, which can be seen in FIGS. 26 and 27.)The substrate 2525 bearing the RFID tags 2420 is lined up such that thatthe top of the RFID tags 2420 line up with the bottom edge of the secondmicrostrip transmission line 2515, but the RFID tags 2420 do not layacross the top of the second microstrip transmission line 2515 (which,again, is not visible in FIG. 26, as it is covered by the substrate2525).

FIG. 27 contains an illustration of the prototype of FIGS. 24-26combined with a screen shot of software displaying the results of a testof the prototype. Near the top of FIG. 27, a schematic diagram depictsthat the substrate 2525 is properly positioned over the secondtransmission line 2515, leaving part of the second base 2530 exposed.Near the top of FIG. 27, a schematic diagram of a hand 2700 with twofingers 2705 extended is shown depressing the first and third RFID tags2710 and 2715. In general, RFID tags 2420 are only energized and thusare only read when depressed, and multiple RFID tags 2420 may be read atone time, or in succession so quickly that to the user the reading isseemingly occurring at the same time. In an alternate embodiment, eachRFID tag 2420 further comprises a button configured to be latched upon afirst depression by finger 2705 and unlatched upon a subsequent seconddepression, such that the button when latched holds its state of beingcapable of being energized when operably depressed until it isunlatched. Software such as the multi-reader software sold as Speedway®Gen2 RFID sold commercially by Impinj, Inc., installed on a processorconnected to the RF feed, displays readings from depressed tags. Asoftware display 2720 is depicted in the screenshot of FIG. 27. Thedisplay in the screenshot depicts a line for each of the fifteen RFIDtags 2420 shown in FIG. 27. If an RFID tag 2420 is not being read, theline for that RFID tag 2420 is red in color. Lines representing the RFIDtags being read (2710 and 2715 in this illustration) are displayed inthe color white. The first line 2725 and the third line 2730 in thescreenshot of FIG. 27 are outlined. On the display, the softwareprovides relevant information from the depressed RFID tags 2420 in ablack font with a white background. In this illustrated example, thefirst and third lines 2725 and 2730, respectively, are providingrelevant information, indicating that depression of the correspondingtags 2710 and 2715 are being read successfully.

FIG. 28 depicts a diagram of a ring sensor 2800 which may be used invarious embodiments described herein. The ring sensor 2800 may comprisea source element 2802 such as a microstrip waveguide or a type ofantenna and a conductive ring 2804 connected to an RFID integratedcircuit 2806. While the conductive ring 2804 of FIG. 28 is representedas having a predominantly rectangular shape, the loop of conductive ring2804 may comprise a variety of other shapes, such as circular,elliptical, triangular, square, trapezoidal, polygonal, or any othershape suitable for performing the function of indicating a position inrelation to the source element 2802.

FIG. 29a depicts a diagram of a ring sensor 2900 a, which may be used invarious embodiments described herein. The ring sensor 2900 a comprises asource element 2902, which might be a microstrip waveguide or a type ofantenna, and a conductive ring 2904 a connected to an RFID integratedcircuit 2906 a. An RFID interrogator (shown generally in FIG. 1 asinterrogator 145 although not shown in FIG. 29a ) communicates with theRFID integrated circuit 2906 a when the position and rotation of thering 2904 a is suitable for coupling to the source element 2902. In thisgeneral sense, the source element 2902 and ring 2904 a can be used as asensor to detect when the ring 2904 a has been moved laterally into theenabling position (as shown), vertically, or in general a combination oflateral and vertical positioning (both not shown). In addition, the ring2904 a will not generally couple well when the orientation of the ringedges are not predominantly aligned with the source element 2902. Forexample in FIG. 29a , the ring 2904 a will couple to the source element2902, whereas in FIG. 29b , the ring 2904 b has been rotated about anx-axis such that it no longer couples with the source element 2902.While the conductive ring 2904 a of FIG. 29a and the conductive ring2904 b of FIG. 29b are each represented as having a predominantlyrectangular shape, the conductive rings 2904 a and 2904 b of FIGS.29a-29b may have a variety of other shapes, such as circular,elliptical, triangular, square, trapezoidal, polygonal, or any othershape suitable for performing the function of indicating a position inrelation to the source element 2902.

FIGS. 30a and 30b are diagrams of a two-part RFID ring tag 3000 used asa sensor to detect whether a hinged door is in an open or closedposition, with FIG. 30b comprising a diagram of the two-part RFID ringtag 3000 installed on a door hinge. The two-part RFID ring tag 3000comprises a ring circuit 3005 and an antenna 3010. When the two-partRFID ring tag 3000 door is installed on the door hinge as depicted inFIG. 30b and the door is closed, the ring circuit 3005 is suitably closeto the antenna 3010 such that the antenna 3010 couples energy to thering circuit 3005. An interrogator (shown generally as interrogator 145of FIG. 1 although not depicted in FIG. 30a or 30 b) is able to sendinformation to, and receive information from, the energized ring circuit3005 of the two-part RFID ring tag 3000, signaling that the door isclosed.

FIGS. 31a and 31b depict another embodiment described herein. In thisembodiment, a ring sensor 3100 is used as a switch. The ring sensor orswitch 3100 comprises a ring tag 3104 with an RFID integrated circuit3106 operatively connected thereto. The ring tag 3104 is attached to amembrane 3103 that pivots about a rotational axis 3110. In FIG. 31a ,the membrane 3103 is in the “off” state such that the ring tag 3104 isnot enabled to couple energy to and from a source element 3102, whichmight be, for example, a meandered dipole or a microstrip patch antenna.When the membrane 3103 is rotated about the rotational axis 3110, asshown in FIG. 31b , however, the ring tag 3104 is enabled and canreceive energy from, or transmit energy to, an interrogator (showngenerally as interrogator 145 of FIG. 1 although not shown in FIG. 31aor 31 b). The membrane 3103 may be fastened at one or both ends by alatch, a hook-and-loop fastener (commonly referred to as “Velcro”, amagnet, or any of a number of other fastening elements, including anadhesive (although not depicted in FIG. 31a or 31 b). The membrane 3103might be an insulating fabric or rigid insulating element. In oneembodiment, the membrane 3103 comprises a strip of insulating fabric,the source element 3102 comprises a fabric antenna, and a section of ahook-and-loop fastener is used to fasten the end of the membrane 3103 ineither the “off” or “on” position. An array of similar switches may beworn on a shirt and used to communicate commands or other information toa processor through an RFID interrogator.

Any of a number of other switch mechanisms is possible with a variety ofoptions to captivate the ring sensor in both “off” positions, whichdisable communications to the tag, and “on” positions, which enablecommunications to a tag.

In light of the principles and exemplary embodiments described andillustrated herein, it will be recognized that the exemplary embodimentscan be modified in arrangement and detail without departing from suchprinciples. Also, the foregoing discussion has focused on particularembodiments, but other configurations are contemplated. In particular,even though expressions such as “in one embodiment,” “in anotherembodiment,” “in a version of the embodiment” or the like are usedherein, these phrases are meant to generally reference the range ofpossibilities of embodiments, and are not intended to limit thedisclosure to the particular embodiments and configurations describedherein. As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments.

Similarly, although exemplary processes have been described with regardto particular operations performed in a particular sequence, numerousmodifications could be applied to those processes to derive numerousalternative embodiments of the present disclosure. For example,alternative embodiments may include processes that use fewer than all ofthe disclosed operations, processes that use additional operations, andprocesses in which the individual operations disclosed herein arecombined, subdivided, rearranged, or otherwise altered.

In view of the wide variety of useful permutations that may be readilyderived from the exemplary embodiments described herein, this detaileddescription is intended to be illustrative only, and should not be takenas limiting the scope of the disclosure. What is claimed as thedisclosure, therefore, are all implementations that come within thescope of the following claims, and all equivalents to suchimplementations. In the claims, means-plus-function andstep-plus-function clauses are intended to cover the structures or actsdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, while anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures.

What is claimed is:
 1. A radio frequency identification (RFID)-enabled pressure sensing apparatus, comprising: a plurality of RFID tags attached to an operatively insulating and compressible substrate; a collector in communication with the plurality of RFID tags; an operably planar open waveguide, the waveguide being bonded on an operatively insulating dielectric base and in communication with the collector; and a load connected to one end of the waveguide, wherein the substrate having the plurality of RFID tags attached thereto is positioned over the dielectric base and adjacent to the waveguide, one or more of the plurality of RFID tags being energized when operably depressed to enable an electromagnetic coupling between the waveguide, allowing the operably depressed RFID tag to send signals via the collector to an interrogator.
 2. The apparatus of claim 1, wherein the waveguide comprises a top microstrip line and a conductive ground plane beneath the dielectric base.
 3. The apparatus of claim 1, wherein each RFID tag comprises a closed conductive path operatively connected with an RFID integrated circuit and wherein at least part of the closed conductive path is laterally adjacent to the top microstrip line such that depression of the RFID tag permits energizing of the RFID integrated circuit by the electromagnetic coupling resulting thereby.
 4. The apparatus of claim 1, wherein the waveguide comprises a coplanar waveguide and the RFID tag comprises a conductive ring with an integrated circuit positioned on the substrate within a gap in the coplanar waveguide.
 5. The apparatus of claim 1, wherein the waveguide comprises a twin transmission line.
 6. The apparatus of claim 1, wherein the waveguide comprises a slot disposed between two conductive regions, one RFID tag on the substrate positioned within the slot such that an RFID integrated circuit of the positioned RFID tag is energized when the substrate is depressed.
 7. The apparatus of claim 1, wherein impedance of the load is substantially matched to impedance of the waveguide in order to substantially suppress any standing waves.
 8. The apparatus of claim 1, wherein impedance of the load is substantially an open or short circuit relative to impedance of the waveguide in order to enhance a standing wave.
 9. The apparatus in claim 1, wherein the collector is an antenna.
 10. The apparatus in claim 1, wherein the collector is an interface directly to the RFID interrogator.
 11. The apparatus in claim 1, wherein each RFID tag comprises a button configured to be latched upon a first depression and unlatched upon a subsequent second depression, such that the button when latched holds its state of being capable of being energized until it is unlatched.
 12. The apparatus in claim 1, wherein the dielectric base and the waveguide bonded thereto are formed from non-conductive and conductive fabrics, respectively, and the compressible substrate is made of pressure-sensitive memory foam.
 13. A radio frequency identification (RFID)-enabled pressure sensitive keypad comprising: a plurality of RFID tags bonded to an operatively insulating and compressible substrate; an operably planar open waveguide, the waveguide being bonded on an operatively insulating dielectric base and in communication with a collector; and a load connected to one end of the waveguide, wherein the substrate having the RFID tags bonded thereto is positioned over the base and adjacent to a conductor of the waveguide whereby depression of one of the RFID tags enables an electromagnetic coupling between the waveguide and the depressed RFID tag such that the depressed RFID tag is energized and thereby sends signals via the collector to an interrogator.
 14. The apparatus of claim 13, wherein the waveguide comprises a top microstrip line and a conductive ground plane beneath the dielectric base.
 15. The apparatus of claim 14, wherein each RFID tag comprises a closed conductive path operatively connected with an RFID integrated circuit and wherein at least part of the closed conductive path is laterally adjacent to the top microstrip line such that depression of the RFID tag permits energizing of the RFID integrated circuit by the electromagnetic coupling resulting thereby.
 16. The apparatus of claim 13, wherein the waveguide comprises a coplanar waveguide and the RFID tag comprises a conductive ring with an integrated circuit positioned on the substrate within a gap in the coplanar waveguide.
 17. The apparatus of claim 13, wherein the waveguide comprises a twin transmission line.
 18. The apparatus of claim 13, wherein the waveguide comprises a slot disposed between two conductive regions, one RFID tag on the substrate positioned within the slot such that an RFID integrated circuit of the positioned RFID tag is energized when the substrate is depressed.
 19. The apparatus of claim 13, wherein impedance of the load is substantially matched to impedance of the waveguide in order to substantially suppress any standing waves.
 20. The apparatus of claim 13, wherein impedance of the load is substantially an open or short circuit relative to impedance of the waveguide in order to enhance a standing wave.
 21. The apparatus in claim 13, wherein each RFID tag comprises a button configured to be latched upon a first depression and unlatched upon a subsequent second depression, such that the button when latched holds its state of being capable of being energized until it is unlatched.
 22. The apparatus in claim 13, wherein the dielectric base and the waveguide bonded thereto are formed from non-conductive and conductive fabrics, respectively, and the compressible substrate is made of pressure-sensitive memory foam. 